We have developed an HPLC method for the quantitation of polysaccharide (PS) in Hib conjugate vaccines. The HPLC method could quantitate as low as 0.1 mg of Hib PS. This method has been successfully used to quantitate the PS content of Hib conjugate in Merck's PedvaxHIB vaccine in which the lactose stabilizer interferes with the colorimetric ribose assay for the determination of the PS content. Recently we further explored the method to determine the PS content of Hib conjugate in the combination vaccines such as Lederle's Tetramune and Merck's COMVAX vaccines which contain an Hib conjugate as a component in the vaccines. Preliminary results indicated that the HPLC method could also be used to quantitate the PS content of Hib conjugates in these combination vaccines.